Malignant transformation of struma ovarii into follicular thyroid carcinoma: A case report

Struma ovarii is a rare form of mature cystic teratoma, with malignant transformation reported in approximately 5% to 10% of cases. Transformation into follicular thyroid carcinoma (FTC) is extremely uncommon; as a result, no standardized guidelines exist for treatment or prognosis for such cases.

A 54-year-old woman with cholelithiasis presented with upper abdominal discomfort. A lower abdominal mass was incidentally detected during evaluation.

Transvaginal ultrasonography revealed a 12-cm multilocular cystic tumor in the right ovary. Magnetic resonance imaging and computed tomography findings suggested a mature cystic teratoma with potential for malignant transformation. Exploratory laparotomy was performed, and intraoperative frozen section analysis confirmed malignant transformation.

The patient subsequently underwent total abdominal hysterectomy, bilateral salpingo-oophorectomy, pelvic lymphadenectomy, para-aortic lymph node biopsy, and omentectomy. Histopathological examination revealed tumor cells demonstrating cribriform proliferation, accompanied by eosinophilic structures, extensive necrosis, and venous invasion. These findings supported the diagnosis of FTC arising within struma ovarii.

Postoperatively, the patient underwent routine follow-up, including serum thyroglobulin tests and imaging studies every 3 months. At 1 year, the patient showed no signs of tumor recurrence and remained in good clinical condition.

Malignant transformation of struma ovarii into FTC is an extremely rare condition and necessitates thorough histopathological evaluation for accurate diagnosis. This case highlights the diagnostic and therapeutic challenges associated with such tumors.